There is a constant demand for electronic devices having smaller features that are more densely crowded together on a single substrate or chip. At the same time, consumers of such devices are demanding faster operating speeds and higher reliability, such as are achieved with monolithic microwave integrated circuits (MMICs). Monolithic microwave integrated circuits are formed of a plurality of devices or circuit components that are fabricated on a single semiconductor substrate, and are designed to operate at microwave frequencies, which are generally regarded to be between about 3,000 and 300,000 microns, corresponding to operating frequencies of from about 1 to about 100 gigahertz (GHz).
As is well known to those who design integrated circuits or use integrated circuits in the design of various electronic packages, the performance characteristics of electronic devices operating in the microwave frequency range are highly susceptible to deleterious effects caused by stray capacitances and inductances that can be generated at wire bonds of the type that have been conventionally used to electrically connect terminals of an integrated circuit device to a substrate (e.g., a printed circuit board) or another integrated circuit device.
In order to reduce stray capacitances and inductances, surface mount chip technology that eliminates wire bonding has been utilized. Flip chips are a type of integrated circuit device that is surface mounted and does not require any wire bonds. Instead, the flip chip has solder beads (also referred to as solder bumps or solder balls) on the terminals (also referred to as I/O pads) of the integrated circuit device. The solder beads are typically located around the perimeter or full array of the device, and are mounted to a substrate such as a printed circuit board or other package carrier by positioning the solder beads in registry with appropriate contact pads on the substrate, and heating the solder beads following an appropriate temperature profile to cause reflow of the solder beads. Upon subsequent cooling, wireless interconnections between the integrated circuit device and a circuit pattern defined on the substrate are formed. The use of flip chip technology has several recognized advantages, including reduced signal inductances, reduced power/ground inductances, higher signal density, reduced package footprint and better accuracy due to self-alignment of die by solder bumps.
The use of carbon nanotube technology in the fabrication of integrated circuits has been proposed. For example, U.S. Pat. No. 6,933,222 describes integrated circuits comprising layers of arrays of carbon nanotubes separated by dielectric layers with conductive traces formed within the dielectric layers to electrically interconnect individual carbon nanotubes. The integrated circuit devices are fabricated by selectively depositing carbon nanotubes onto catalysts selectively formed on a conductive layer at the bottom of openings in a dielectric layer. The use of carbon nanotube electrical conductors in these devices is limited to the provision of electrical connections between different circuit layers of an integrated circuit having multiple circuit layers.